Polymer product for treating leather

ABSTRACT

The invention concerns graft copolymers, useful for the treatment of leather, comprising monomers of the formula ##STR1## grafted onto a base polymer comprising monomers of the formula ##STR2## wherein R 1  and R 2  stand for a hydrocarbon group having 2 to 24 carbon atoms, with the proviso that the groups R 1  and R 2  have van der Waals volumes which differ from one another by less than 30 percent.

The present invention relates to polymer products for the treatment ofleather, consisting of graft copolymers comprising acrylate andmethacrylate polymers, and to methods for treating leather with theseproducts.

Polymer dispersions comprising acrylates play a significant role in thedressing of leather. Polymer products comprising polyacrylates are usedboth for impregnation and grounding and also, more recently, haveincreasingly been used for top coating [cf. J. A. Handscomb, J. Soc.Leather Trades Chem. 43, 237 (1959); Ch. Cluthe et al., J. Am. LeatherChem. Assoc., 73(1), 22-29 (1978); DE-A 33 44 254; U.S. Pat. No.4,491,645].

Polyurethane dispersions, acrylate-butadiene dispersions, polyvinylchloride/polyvinyl acetate dispersions, nitrocellulose emulsions, interalia, are also of significance in the dressing of leather. Although thenumber of acrylate dispersions used in leather dressing has reached ahigh level, nevertheless they have only limited usefulness at variouspoints. The reasons for this are probably first to be sought in certaininherent material properties which in these cases have a negativeeffect, e.g. a high thermal plasticity which makes itself evident in apoor susceptibility of the leather to stamping. For many uses, e.g. ingrounding, an often too strong tackiness of the acrylate film has proveddisadvantageous. The mechanical properties of films of acrylatedispersions, such as extension to break and tensile strength, are toosmall to meet high demands, a condition which exhibits itself as aninsufficient resistance to flexing (e.g. in the Bally-Flexometer test).Also problematic are their resistance to water and solvents, which ismore strongly evident, e.g., for polyurethane dispersions.

Thus, there was a need for improved polymer products comprisingpolyacrylates and polymethacrylates [hereinafter "poly(meth)acrylates"]for the treatment, particularly the dressing, of leather, which wouldavoid the disadvantages observed in the leather treating field whileretaining the otherwise advantageous spectrum of properties of(meth)acrylate polymers.

It has now been found that, surprisingly, the requirement of thetechnology are particularly well met by graft polymers comprising(meth)acrylate, in which a graft monomer of the formula (I) ##STR3##where R₁ stands for a hydrocarbon group, particularly an alkyl group,having 2-24 carbon atoms, preferably 2-8 carbon atoms, especially for C₂-C₄ -alkyl, and particularly for ethyl, butyl, and isobutyl, is graftedonto a base or "backbone" polymer including 55-100 percent by weight,particularly 85-100 percent by weight of monomers of the formula (II)##STR4## where R₂ stands for a hydrocarbon group having 2-24 carbonatoms, preferably 2-8 carbon atoms, particularly an alkyl group, andparticularly for the groups ethyl, butyl, and 2-ethylhexyl, with theproviso that the groups R₁ and R₂ have van der Waals volumes which aredifferent by less than 30 percent of the larger volume. [For adiscussion of van der Waals volumes and atomic radii, and particularlyvarious atomic group contributions to the van der Waals volume ofhydrocarbons, see A. Bondi, "van der Waals Volumes and Radii", J. Phys.Chem. 68, 441-451 (1964), further discussed by M. Charton, J. Am. Chem.Soc. 91(3), 615-618 (1968). Some volumes are tabulated in standardreference works such as the Handbook of Chemistry and Physics, 57thEdition, R. C. Weast, editor, page D-178, CRC Press 1977.]

It is advantageous if the condition prevails that the heats of mixing ofthe hydrogenated monomer components of the formula (I-hydr) ##STR5## andof the hydrated monomer components of the formula (II-hydr)

    CH.sub.3 --CH.sub.2 --COOR.sub.2 (II-hydr)

wherein R₁ and R₂ have the aforementioned meanings, are in each caseless than 100 cal/mol of mixture.

The van der Waals volumes according to Bondi, loc. cit., are preferablyless than 20 percent.

Determination of the heats of mixing of the hydrated monomercompositions is in general not absolutely necessary because in a seriesof instances they can be found directly in comprehensive tabulatedvalues. Reference is made to the monograph Mischungswarmen vonFlussigkeiten ("Heats of Mixing of Liquids"), by W. P. Belousow and A.G. Moratschewski, Verlag Chemie, Leningrad (1970).

By definition, R₁ and R₂ in the formulas (I), (II), (I-hydr), and(II-hydr) stand for a hydrocarbon group having at least 2-24 carbonatoms, preferably for an acyclic, optionally branched, alkyl group,particularly having at least 2 and up to 8 carbon atoms, or for a cyclichydrocarbon group having 5 to 12 ring members, particularly an alicyclicgroup.

A series of suitable I/II combinations can be taken from DE-OS 37 08 427(=U.S. Pat. No. 4,900,791, incorporated herein be reference). Polymermixtures of polyacrylates and polymethacrylates are described there. Itis also advantageous to graft monomers from the series ofpolymethacrylates named in DE-OS 37 08 427 onto the polyacrylates whichare compatible with these polymethacrylates.

It should further be explained that the monomers which are involved inthe structure of the base or backbone polymer usually stand in a weightratio of 10 to 90 to 90 to 10, preferably 90 to 50 to 50 to 10, and inthe particularly preferred ratio 60 to 40 to 80 to 20 to the graftmonomers.

In addition to the monomers of formula (I), further suitably selectedmonomers can be co-grafted, for example other methacrylic acid esters,particularly preferably methyl methacrylate, which can be contained inamounts from 0-80 percent by weight, preferably in amounts of 10-60percent by weight, and very particularly preferably in amounts from 15to 40 percent by weight of the graft monomers. In the same way, it ispossible to co-graft acrylic acid esters, e.g. methyl acrylate or ethylacrylate in amounts from 0.1 to 10 percent by weight, preferably 0.2-5percent by weight.

The amount of functional comonomers such, as methylol methacrylamide,methacrylic acid, or methacrylamide should be less than 5 percent byweight. Preferably, the mixture of graft monomers contains no glycidylmethacrylate and no maleic acid anhydride. Likewise, the amount ofstyrene, acrylonitrile, and monomers containing halogen in the graftmonomer mixture should be less than 10 percent by weight, preferablyless than 1 percent by weight, and particularly preferably at 0 percentby weight. In general, the molecular weight of the base polymer(determined by viscosimetry or light scattering) is in the range from200,000 to 1,000,000,000, preferably up to 10,000,000. The base polymersare preferably also not crosslinked after grafting. Nevertheless, it canhappen that the original high-polymeric non-crosslinked base polymer isslightly crosslinked by the grafting thereon of the graft monomermixture (the amount of crosslinking points is less than 0.01 percent byweight, preferably less than 0.001 percent by weight). High-polymericnon-crosslinked base polymers are very particularly preferred. Incontrast, the grafted branches, i.e. the graft polymers grafted onto thebase polymer are essentially shorter-chained. In general, the molecularcontent of the graft branches is from 1,000-1,000,000 Daltons,preferably 2,000-500,000, and particularly preferably 5,000-200,000. Ingeneral 10-100 percent by weight (particularly 20- 95 percent by weight)of the total graft monomers are grafted onto the grafting support.

The base polymer preferably consists of 55-100 percent by weight, morepreferably from 85-100 percent by weight, and most preferably of 91-100percent by weight of monomers having formula II.

As further monomers, the base polymers can contain other monomerscopolymerizable with acrylic acid esters in amounts equal to or lessthan 45 percent by weight, preferably in amount less than 15, and mostpreferably in amounts less than 9 percent by weight and to 0.1 percentby weight: Here, methacrylic acid esters are particularly to be named.Accordingly, it is preferred to proceed from mixtures of two differentmonomers of the formula II. The base polymer can contain styrene inamounts up to 25 percent by weight, preferably less than 15 percent byweight. Optionally substituted phenyl(alkyl)acrylates deserve specialinterest, for example benzyl acrylate or phenylpropyl acrylate, whichcan be present in amounts from 0-30 percent by weight. Also, methylacrylate can be copolymerized in amounts up to 45 percent by weight inthe synthesis of the base polymer. Amounts of hydrophilic monomers suchas hydroxyalkyl acrylate or methacrylic acid can be copolymerized inamounts of 0-5 percent by weight, preferably in amounts of 0-3, and mostpreferably in amounts of 0.1-0.5 percent by weight.

Butadiene or isoprene should generally not be copolymerized and theircontent in the base polymer should be less than 5 percent by weight,with those base polymers which contain neither butadiene nor isoprenebeing particularly preferred. Likewise, as a rule polyfunctionalmethacrylic acid esters such as butanediol dimethacrylate orpolyfunctional acrylic acid esters such as hexanediol diacrylate shouldnot be used in the synthesis of the base or backbone polymers. Theircontent in the base polymers should be limited to less than 0.01 percentby weight. Monomers which actively graft, such as allyl (meth)acrylatesor vinyl (meth)acrylates, e.g. allyl acrylate, in contrast can bepresent in amounts up to 1 percent by weight (preferably in amounts upto 0.3, more preferably up to 0.2, and most preferably up to 0.09percent by weight). Chain transfer agents such as mercaptans, e.g.2-ethylhexyl thioglycolate, must be used (in amounts less than 0.5percent by weight) particularly with large amounts of graft-activemonomers in order to avoid crosslinking of the acrylate polymers. Graftpolymers wherein the hydrocarbon groups R₁ and R₂ signify C₂ -C₄ -alkylhave proved especially suitable in the leather field, particularly forproducts for dressing leather.

Base polymers in which R₂ of formula (II) stands for ethyl (polyethylacrylate) and graft monomers of formula (I) in which R₁ stands for ethyl(ethyl methacrylate) can be held out as a paradigm for the presentinvention. In this case, polyethyl acrylate-polyethyl methacrylate graftpolymers are obtained, for example by a simple polymerization in whichthe monomers are fed in, which polymers form glass-clear, toughsynthetic resin films at room temperature. Likewise, good results areobtained if R₁ =n-butyl and R₂ =isobutyl.

In principle, the relevant polymerization methods of the prior art [cf.H. Rauch-Puntigam, Th. Volker, Acryl-und Methacrylverbindungen ("Acrylicand Methacrylic Compounds"), Springer Verlag 1967; H. F. Mark et al,Encyclopedia of Polymer Science and Engineering, 2nd edition, Vol. 1,265-276, John Wiley & Sons 1985] are suitable for the preparation of thepolymers, wherein for the preparation of the base or backbone polymerconditions are advantageously used with do not promote crosslinking. Asa rule, free radical polymerization employing the usual free radicalinitiators is used.

In every case, the base polymer is prepared first and is then graftedwith the graft monomers in a solvent which shows little tendency fortransfer, e.g. butyl acetate, at the highest possible temperature, e.g.120° C. The grafting of the high molecular weight base polymer directly,in a melt without a solvent, using an extruder or pressure reactor attemperatures from 150° C. to 200° C. is of special interest. In thiscase, the base polymer is preferably first prepared in a solvent or bybulk polymerization to only a small degree of conversion, degassed, andthen grafted with the graft monomers. To achieve easily handled basepolymers, their molecular weight is to be limited to values less than1,000,000, optionally with the addition of chain transfer agents.

For this, above all, preparation by an emulsion polymerization method inan aqueous medium is technically significant. As initiators, thoseconventionally used for this purpose, e.g. potassium- or ammoniumperoxydisulfate are used, generally in amounts of 0.001 to 0.5 percentby weight, based on the monomers, but also, optionally, a redox system(cf. Rauch-Puntigam, loc. cit., pages 221-229). While the use of readilygraftable monomers in the base polymer has advantages, it has proveddisadvantageous to force grafting by the addition of large amounts ofinitiator. This procedure leads to thermally labile polymers.

As emulsifiers, again those known in the art are useful, particularlyanionogens such as the alkali metal salts of paraffin sulfonates, andare normally used in amounts from 0.5-5 percent by weight (based on theamount of water).

The preparation of the graft polymers in a two-stage emulsionpolymerization process, wherein the first stage, the preparation of thebase polymer is advantageously carried out as a batch polymerization, isof particular interest. In this way, it is possible to obtain, forexample, non-crosslinked polyacrylates having a desired high molecularweight (for example having a viscosity number, J=200-1000 ml/g,determined according to ISO 1628-6 or DIN 51562, parts 2 and 3 and DIN7745, part 2) in a particularly easy fashion.

Suitably, the grafting of the graft monomers follows directly thereafteras a polymerization wherein the monomer mixture is run into the reactionmixture over a period of time. This step is advantageously carried outat temperatures of 70° C.-100° C. For this, in particular, one canproceed as follows:

At first an aqueous emulsion of the monomers is prepared, with additionof emulsifiers and of initiators, wherein--as a model--the ratio ofmonomer to water in parts by weight can be about 1:2.

One can advantageously proceed so that at first only the peroxidicpartner of the redox initiator system is added. Then the batch iswarmed, suitably under an inert gas blanket such as of nitrogen/argon toa suitable temperature, for example 35±10° C. with addition of thereducing partner of the redox system. Usually the temperature risessharply within a short time (about 10 minutes is mentioned as a model),to about 85±5° C. Thereafter, the graft monomers are added, preferablydropwise, as a rule within about 15-90 minutes. Subsequently thepolymerization is carried to termination with warming, for example byholding the temperature at about 80 ° C.

The graft copolymer is usually obtained in the form of a stabledispersion having a polymer content usually in the range from 20 to 70percent by weight based on the total dispersion, and can be dried toform a tough elastic film either directly or after the addition ofammonia, for example. The residual monomer content is usually in therange of parts per million.

By variation of the monomers of the base polymer and of the graftmonomers, the hardness or consistency of the films can be influenced andguided in diverse ways. [Concerning the influence of the monomers on the"hardness" of the polymers, see ViewegEsser, Kunststoffhandbuch("Synthetic Resin Handbook"), Vol. IX, Carl Hanser Verlag, 1975; H. F.Mark et al, Encyclopedia of Science & Engineering, 2nd Ed., Vol. 7, pg.533-544, J. Wiley 1987; Kirk-Othmer, Encyclopedia of ChemicalTechnology, 3rd Ed., Vol 1, pg. 387-389, J. Wiley, 1978).]

For the grounding step in leathers, "soft" graft polymers having a filmhardness Shore A20 to A50 are preferably used. (For determination of theShore Hardness, see DIN 53 505 or ASTM D 676).

As a first approximation, film hardness can be adjusted, on the onehand, by selection of the graft monomers and, on the other hand, by theadmixture of "soft" and "hard" graft polymers. As examples for "soft"graft polymers, can be mentioned those containing butyl methacrylateand/or ethylhexyl methacrylate as graft components, which optionally maybe co-grafted with "harder" monomers such as ethyl methacrylate, methylmethacrylate, inter alia. As "harder" graft polymers those with ethylmethacrylate, methyl methacrylate, benzyl methacrylate, as graftcomonomers, optionally in admixture, can be mentioned.

The methods and modalities of the uses of the graft copolymers accordingto the invention are close to those of the state of the art [cf. H.Herfeld, Ed., Bibliothek des Leders ("The Leather Library"), Vol. 6; R.Schubert, Lederzurichtung-Oberflachenbehandlung des Leders ("LeatherDressing-Surface Treatment of Leather"), Umschau 1982, pg. 148-219],just as are the useful leather toppings and brightening auxiliaries andfinishing auxiliaries. Application by spraying, by "airless"spraying,roller coating inter alia are particularly recommended.

The coats of groundings and seasons can be mixed, for example to improvephysical properties such as buckling strength, resistance to water andsolvents, extension, etc. or stampability, with certain additionalpolyurethane dispersions, as well as with crosslinking systemscomprising epoxides, polycarbodiimides, polyisocyanates, orpolyaziridines. These crosslinking systems in general stand in a weightratio of 100 to 10 to 100 to 0.1 with respect to the copolymer product.Practise has shown that the amount of non-grafted polymer dispersion maynot be too high so that the formation of the hard-soft segmentedstructure is not overly disturbed. Thus, as a rule the amount ofnon-grafted polymer dispersion should not exceed 90 percent of the totalpolymer dispersion.

To achieve a minimum film thickness as well as a sufficient coveringeffect, the use of thickening agents known per se is indicated. Asthickeners, for example, are those from the group formed by polyglycolpolyurethanes, polyvinyl pyrrolidone, or acrylate (co)polymers. Ingeneral, the thickeners stand in a weight ratio of 100 to 10 to 100 to0.01 with respect to the graft polymers. By adjustment and adaptation ofthe viscosity, the penetrating power or the degree of covering can bewell controlled. As already discussed, the film hardness and filmconsistency can be extensively steered in the desired direction bysuitable variation of the monomers in the graft- and base polymers, aswell as by selection of the ratio of base polymer to graft polymer. As afurther advantage in connection with usage, particularly in the dressingof leather, it is noted that all conventional auxiliaries, especiallythose commercially available, for regulating hand, color, flow, andviscosity can be used. These are generally solutions (e.g. flow agentproducts comprising glycol ether, ethers such as butyl glycol,methoxypropanol, tributoxyethyl phosphate, etc.) oremulsions/dispersions with casein, waxes, silicones in the amounts orconcentrations usually used [cf. F. Stather, Gerbereichemie undGerbereitechnolgie ("Tanning Chemistry and Tanning Technology"),Akademie Verlag, Berlin, 1967, pages 507-632; R. Schubert, loc. cit.].

In particular, the leather colorants known in the art can be used veryeffectively (cf. F. Stather, loc. cit., pg. 615-632), for example in theform of pigment pastes, also in case of necessity matting agents can beused, for example those comprising silicates.

Particularly outstanding properties of the graft polymers of theinvention which should be mentioned are their relatively smallthermoplasticity and the good tensile and extension properties. In thecoating of leather, this condition shows itself in an outstandingstampability, slight adhesion or good resistance to blocking, as well asin a higher flexibility.

A fundamental prerequisite for the attainment of these properties is atemperinq of the coated material at certain minimum temperatures. Theminimum temperature can be brought into the range of 60° C.-120° C.,advantageous for leather dressing, by way of the composition of thepolymers. Heating may be done with conventional heat sources or by theuse of infrared or microwave radiation.

The tempering time also plays a role in producing optimum properties.Above all, a favorable influence on the aforementioned properties isbrought about during the treatment times conventional for dressing,which are divided into the steps of drying, pressing, and stamping. Inthe case of drying, on the average, for example, 2 to 5 minutes attemperatures in the range from 60° C.-90° C. are to be added on. Thestatic and dynamic procedures of ironing and stamping follow attemperatures between 70° C. and 170° C., as a rule applied during a fewseconds, as a model 2-6 seconds may be mentioned, under pressures of50-300 bar.

In general it can be said that the physical properties of the coatingcan additionally be raised by extension of the tempering time. Inpractise, one advantageously proceeds so that the aqueous polymerdispersions can be used in the form in which they are prepared.

For making dressings, the graft polymer, preferably in dispersion form,is used as the starting point. To it, water and then the additives, suchas matting agents, casein-fat emulsion, then the aqueous paraffinemulsion, also the pigment paste and the coalescing agent, the siliconemulsion and, at last, optional thickening agent are added withstirring.

According to this procedure, two formulations, a) and b) are prepared(for a summary, see Table 1.)

EXAMPLES

A-1: Use as Grounding for Full-Grain Nappa Leather

Formulations a) or b) are sprayed on once or twice to saturation (20-40g/m²) using a commercially available compressed air spray gun (about 4bar pressure, nozzle breadth 1.2 or 1.4 mm). This is followed by dryingeither at 60° C.-80° C. in a drying tunnel for 1-5 minutes withcirculation of heated air or at room temperature. (Alternatively,heating could be by microwave or infrared radiation.) This is followedby ironing at 80° C.-90° C. with a pressure of 50-100 bar. Then thepiece is sprayed twice more with the relevant formulation at mediumcoverage (about 10-20 g/m²) and dried as described above.

The total amount of material applied amounts to 60-100 g/m². The resultsare reported in Table 2.

A-2: Use as Grounding for Buffed Furniture Leather

Formulations a) or b) are sprayed on twice, if desired "airlessly", withgood coverage (75-125 g/m²). Drying follows as under A-1. Then anintermediate lacquer (nitrocellulose emulsion) is sprayed on, followedby drying [see (A-1)], and finally the piece is stamped at a temperatureof 90° C., at a pressure of 250 bar, for a duration of 3 seconds. Astamping plate having an medium pore grain is used. The piece was againsprayed at medium strength (25-50 g/m²), dried, and then milled for 8hours.

The total amount applied was 200-300 g/m². The results are reported inTable 2.

A-3: Use as Grounding for Tanned Splits

The formulations a) or b) are applied once by means of roller coatingwith recipricol strokes (100-175 g/m².) The piece is then ironed at 90°C. and 150 bar for 3 seconds, followed by a double roller coating firstwith 75-100 g/m² and then with 25-75 g/m². Then a nitrocelluloseemulsion is applied as an intermediate layer. Then the piece is stampedat 90° C. and 250 bar for 3-5 seconds.

The total amount applied amounts to 200-350 g/m². The results arereported in Table 2.

A-4: Use as a Top Coat

In a first step, grounding is accomplished using a conventionalgrounding recipe.

Then, the formulations a) and b) are sprayed on twice. The total amountapplied is 30-60 g/m². The results are evident in Table 2.

                                      TABLE 1                                     __________________________________________________________________________    Examples of Recipes for Grounding- and Top-Coatings on Different Leather      Types                                                                         (in Parts by Weight)                                                                            A-1       A-2        A-3       A-4                                            Grouding for Full                                                                       Grounding for Buffed                                                                     Grounding for                                                                           Application                  Test              Grained Nappa                                                                           Furniture Leather                                                                        Tanned Splits                                                                           as a Top Coat                Leather Type      a)   b)   a)   b)    a)   b)   a)  b                        __________________________________________________________________________    Black pigment Paste (35%)                                                                       100  150  120  150   120  150  --  --                       Aqueous casein-fat                                                                              --   --    40  60     80  --   --  --                       Emulsion (20%)                                                                Aqueous Paraffin   40   60   40  20     20  --   20-50                                                                             20-50                    Emulsion (22%)                                                                Aqueous Matting Paste                                                                           0-30 0-50  0-50                                                                               0-50  0-50                                                                               0-50                                                                               0-20                                                                              0-20                    Comprising Silicic                                                            Acid (30%)                                                                    Water             to 1000 (with preceding ingredients)                        Aqueous Polyurethane                                                                            --   --   --   40    --    50  --    20                     Dispersion (35%)                                                              Acrylate Dispersion of any                                                                      200  300  450  410   600  550  300 280                      of Ex. B(1)-B(3) (40%)                                                        (Shore-Hardness A20-A50)                                                      With Thickener (Acrylic Acid                                                                    --   --   x    x     x    x    --  --                       Copolymer) of Viscosity                                                       16-22 (Measured in Ford Beaker                                                with 4 mm Nozzle) Depending                                                   on Absorptive Capacity of Leather                                             Coalescing Agent Comprising                                                                     --   --   --   --    --   --   10-15                                                                             10-15                    Glycol Ether (100%)                                                           Aqueous Silicone Emulsion (30%)                                                                 0-20 0-20  0-20                                                                               0-20  0-20                                                                              --   0-5 0-5                      Total Amount Applied in g/m.sup.2                                                               60-110                                                                             80-120                                                                             200-300                                                                            200-300                                                                             200-350                                                                            200-350                                                                            30-60                                                                             30-60                    in 2-4 Working Operations                                                     __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Physical Properties of the Dressed Leather of Table 1                                                               Rubbing Resistance.sup.1                                  Flexometer (dry).sup.2                                                                  Flexometer (wet).sup.2                                                                  (VESLIC wet)                            1 = Drying at room temperature                                                                  (Number of Folds)                                                                       (Number of Folds)                                                                       (Number of Rubbings)                    2 = Drying 10 minutes at 90° C.                                                          1    2    1    2    1    2                                  __________________________________________________________________________    A-1                                                                           Full Grain Nappa Leather                                                                      a)                                                                              30,000                                                                              70,000                                                                            20,000                                                                             >50,000                                                                            100-150                                                                            200-300                            (0.8-0.9 mm thick, without                                                                      to   to   to                                                Top Coat          50,000                                                                             100,000                                                                            30,000                                                            b)                                                                              30,000                                                                              70,000                                                                            20,000                                                                             >50,000                                                                            100-150                                                                            200-300                                              to   to   to                                                                  50,000                                                                             100,000                                                                            30,000                                            A-2                                                                           Buffed Furniture Leather                                                                      a)                                                                              20,000                                                                              70,000                                                                            20,000                                                                             50,000                                                                             200  400                                (1-1.1 mm thick, without                                                                        to   to                                                     Top Coat          40,000                                                                             100,000                                                                b)                                                                              20,000                                                                              70,000                                                                            20,000                                                                             50,000                                                                             200  400                                                  to   to                                                                       40,000                                                                             100,000                                                A-3                                                                           Tanned Splits   a)                                                                              20,000                                                                              60,000                                                                            10,000                                                                             40,000                                                                             --   --                                 (1.8-2.0 m thick,                                                                             b)                                                                              30,000                                                                              50,000                                                                            20,000                                                                             40,000                                                                             --   --                                 without Top Coat                                                              A-4                                                                           Values with Top Coat                                                                          a)                                                                              --   --   --   --   150  300                                                b)                                                                              --   --   --   --   150  400                                __________________________________________________________________________     .sup.1 Testing on VESLIC Rubbing Resistance Apparatus with wet felt           according to DIN 53 339                                                       .sup.2 Test of Continuous Fold Resistance with dry or wet leather             according to DIN 53 351                                                  

The graft copolymers according to the invention can be prepared, forexample, according to the following Examples.

B-(1): Graft copolymer comprising a base polymer of ethylacrylate/methacrylic acid grafted with ethyl methacrylate in a weightratio (69.65:0.35):30

An emulsion of 300 g of ethyl acrylate, 1.51 g of methacrylic acid, 3.1g of the sodium salt of C₁₅ -paraffin sulfonate as an emulsifier, 0.62 gof ammonium peroxydisulfate, 0.8 mg of FeSO₄, and 566 g of water iswarmed to 30° C. and combined under an inert gas (nitrogen or argon)with 0.31 g of Na₂ S₂ O₅. The temperature rises within 8-10 minutes to103° C. Immediately thereafter, 129 g of ethyl methacrylate are addeddropwise over 15 minutes. For final polymerization, the batch is stirredfor 60 minutes at 90° C., then cooled.

A stabile dispersion is obtained which can be dried directly or afteraddition of NH₃ to form a tough elastic film. After drying in a dryingcabinet at 90° C., a transparent film is obtained. For furthercharacterization, see Table 3.

B-(2): Graft copolymer comprises a base polymer of ethylacrylate/methacrylic acid grafted with ethyl methacrylate in a weightratio (72.75:2.25):25

As in Example B-(1), an emulsion of 304 g of ethyl acrylate, 9.39 g ofmethacrylic acid, 3.1 g of the sodium salt of a C₁₅ -paraffin sulfonate,with 0.63 g of ammonium peroxydisulfate and 0.8 mg FeSO₄ as well as 0.31g Na₂ S₂ O₅ is polymerized in 587 g of water and 104 g of ethylmethacrylate is grafted thereon.

B-(3): Graft copolymer comprising a base polymer of ethyl acrylate/butylacrylate/methacrylic acid grafted with ethyl methacrylate in a weightratio (65.25:7.5:2.25):25

As in Example B-(1), an emulsion of 273 g of ethyl acrylate, 31.3 g ofbutyl acrylate, 9.39 g of methacrylic acid, 3.1 g of the sodium salt ofa C₁₅ -paraffin sulfonate is polymerized in 566 g of water with 0.62 gof ammonium peroxydisulfate and 0.78 mg FeSO₄ as well as 0.31 g of Na₂S₂ O₅. 104 of ethyl are polymerized thereon by grafting.

Determination of the tensile strength of the films is made according toDIN 53 455 or ISO/R 527, of extension to break according to DIN 53 455,of Shore-D-Hardness according to DIN 53 505.

B-(4): Crosslinked graft copolymer comprising ethyl acrylate/allylmethacrylate grafted with ethyl methacrylate in a weight ratio(69.85:0.15):30

As in Example B(1) an emulsion of 300 g of ethyl acrylate, 0.63 g ofallyl methacrylate, 3.1 g of the sodium salt of a C₁₅ paraffin sulfonateand 0.63 g of ammonium peroxydisulfate, 0.8 mg of FeSO₄, and 0.31 g ofNa₂ S₂ O₅ in 600 g of water is polymerized and 129 g of ethylmethacrylate are grafted onto the base polymer formed.

                  TABLE 3                                                         ______________________________________                                        Example Tensile Strength                                                                           Extension to Break                                                                           Shore-                                    No.     [MPa}        [%]            Hardness                                  ______________________________________                                        B-(1)   8.31         970            81                                        B-(2)   6.8          900            60                                        B-(3)   5.6          750            55                                        B-(4)   10           690            --                                        ______________________________________                                    

B(5): Graft copolymer of 2-ethylhexyl acrylate/methacrylic acid graftedwith 2-ethylhexyl methacrylate in a weight ratio (68:2):30

As in Example B(1), an emulsion of 238 g of 2-ethylhexyl acrylate, 7 gof methacrylic acid, 2.63 g of the sodium salt of a C₁₅ -paraffinsulfonate with 0.53 g of ammonium peroxydisulfate and 0.8 mg of FeSO₄,as well as 0.26 g of Na₂ S₂ O₅ in 592 g of water is polymerized and 105g of 2-ethylhexyl methacrylate are grafted onto base polymer so formed.

What is claimed is:
 1. A graft copolymer, adaptable to the treatment ofleather, comprising the product obtained by grafting monomers comprisingat least one methacrylate ester graft monomer of the formula ##STR6##wherein R₁ stands for a hydrocarbon group having 2-24 carbon atoms, ontoa compatible non-crosslinked acrylate ester base polymer comprising55-100 percent by weight of at least one monomer of the formula ##STR7##wherein R₂ stands for a hydrocarbon group having 2 to 24 carbon atoms,and less than 0.01 percent by weight of polyfunctional esters, with theproviso that the groups R₁ and R₂ have van der Waals volumes whichdiffer from one another by less than 30 percent of the value of thelarger volume, whereby compatibility of the graft monomers and basepolymer is assured.
 2. A graft copolymer as in claim 1 wherein R₁ is aC₂ -C₈ -alkyl group.
 3. A graft copolymer as in claim 1 wherein R₁ R₂ isa C₂ -C₈ -alkyl group.
 4. A graft copolymer as in claim 1 wherein themonomers forming the base polymer stand in a weight ratio of 10:90 to90:10 to the graft monomers.
 5. A graft copolymer as in claim 1 presentin an aqueous dispersion having a polymer content between 20 and 70percent by weight.